The invention herein is directed to a laminated sheet material used in packaging for electrically sensitive components such as electronic components. Many electronic components such as metal oxide semi-conductor devices are sensitive to electrostatic discharges when in their component form and can be damaged by such electrostatic discharges prior to the components being installed in an electronic circuit.
Currently there are several commercially available packaging products made from laminated sheets for electrically shielding electronic components. One of such products is an antistatic shield bag manufactured and distributed by Minnesota Mining and Manufacturing Company. The envelope or package is described in U.S. Pat. No. 4,154,344. The envelope disclosed therein is constructed from a flexible material generally consisting of a laminated sheet material which can be folded upon itself. The inner surface of the envelope is an antistatic layer which is bonded to a carrier sheet and onto which is bonded a conductive metal layer. The metal layer can be coated with a protective coating to protect the metal layer from abrasion. Such an envelope provides a low surface resistivity that exhibits static dissipation and static shielding for components placed in the bag. A disadvantage of such a structure is that the protective coating can be violated exposing the metal layer to potential abrasion. If the conductive metallized layer is violated, the static dissipation or static shielding effect is lost in the area wherein the conductive metallized layer has been abraded. Abrasion of the metallized layer can occur during normal packaging and shipping of such envelopes. Therefore, such envelopes still require some degree of care and caution in handling and shipment in order to protect the sensitive electronic components.
Another product currently commercially available is the Ameri-Stat brand of static shielding bag made by American Hospital Supply Corporation. Such a shielding bag has one metallized shielding layer providing a conductive layer for dissipating static electricity. However, in the structure the metallized layer is buried within the laminated material comprising the sidewall of the envelope. The laminated sidewall has an inner antistatic layer of a polyethylene to which is bonded a metallized conductive layer using a polyurethane adhesive. A substrate or carrier layer is bonded over the metal layer. The substrate layer provides the backbone and general supporting film for the overall flexible sheet itself. The substrate layer can be any suitable material such as a polyester. An antistatic topical coating is applied over the substrate film. Such a structure readily protects the metallized layer. However, the surface resistivity on the outer layers is greater than that of shield bags wherein the metallized layer is on the outer surface of the substrate or carrier film. Since the outer layers are less conductive, they do not provide as low of a surface resistivity for providing static dissipation.
It would be desirable to provide a flexible sheet of material which could be used to create packaging for sensitive electrical components such as sensitive electronic componentry. It would be desirable that such a flexible sheet material be transparent and capable of being sealed upon itself. It would also be desirable to have a flexible sheet material which would provide a low surface resistivity on the outer surface and which would provide a secondary static shielding protection in the event the outer layers are compromised and the static dissipation or static shielding properties of such outer layer are lessened.